This invention relates to the preparation of ether ketones by electrolysis. More specifically, it relates to the oxidation of the hydroxyl moiety contained on a (poly)propylene glycol monoether by electrolysis to prepare an ether ketone.
Houben-Weyl, Methoden der Organischen Chemie, vol. 7/1, pp. 166 and 167, discloses that compounds which in addition to the primary alcohol group contain other groups in most cases, give only very moderate yields when dehydrogenated to the aldehydes. To avoid decomposition reactions, it is necessary to work either at the lowest feasible temperature or, as in the case of the dehydrogenation of tetrahydrofurylcarbinol to tetrahydrofuran-2-aldehyde, to work at a relatively high temperature, with minimum residence time over the catalyst. Thus, when preparing methoxyacetaldehyde, a hydrogen-treated copper oxide catalyst and a reaction temperature of 300.degree. C. are employed. Ethoxyacetaldehyde and butoxyacetaldehyde can also be prepared by a similar method, but in these cases the yields are even worse.
An article in Zh. Prikl. Khim., (Leningrad) 43 (1970), pp. 1132-1136 (English text, pp. 1137-1140), describes a reaction of methyl glycol with air over silver wire spirals as a catalyst, at from 380.degree. C. to 578.degree. C., with yields of from 24.3 to 58 percent, based on starting material. Similar reactions were carried out with butyl glycol at from 463.degree. C. to 488.degree. C. In both cases, reaction temperatures of from 465.degree. C. to 475.degree. C. are regarded as advantageous. A disadvantage of these processes is that notwithstanding the use of reduced pressure, and of equal amounts of nitrogen and air, the maximum achievable yield is only 58 percent.
It is also known (Houben-Weyl, loc. cit., vol. 7/2a, pp. 699-776) that secondary alcohols can be converted to ketones by catalytic dehydrogenation or by oxidation with air. The catalysts generally proposed are both hydrogenation catalysts and dehydrogenation catalysts, especially the above catalysts for the synthesis of aldehydes (loc. cit., p. 700). In general, the dehydrogenation is carried out in the gas phase at from 180.degree. C. to 400.degree. C., in the main at from 200.degree. C. to 250.degree. C. In the synthesis of 1-methoxy-2-oxo-propane, oxidation with chromic acid/sulfuric acid/water mixtures gives a yield of only 29 percent (Houben-Weyl, loc. cit., vol. 7/2a, pp. 722-724).
Dudeck et al., U.S. Pat. No. 4,233,246, Nov. 11, 1980, teach that aliphatic hydroxy carbonyl compounds etherified with aliphatic groups are prepared by oxidizing hydroxy alcohols in the presence of a metal catalyst consisting of one or more layers containing components of silver and copper, with or without added copper/tin/phosphorus or silver alone. The oxidation takes place at temperatures from 450.degree. C. to 700.degree. C.
Wymore, U.S. Pat. No. 4,218,401, Aug. 19, 1980, teaches that primary and secondary alcohols, including alkoxy alkanols, can be oxydehydrogenated to aldehydes and ketones by contacting their vapors mixed with an oxygen-containing gas over a catalyst of rhodium, palladium, platinum, iridium or osmium on a support. The reaction is run at temperatures from 225.degree. C. to 600.degree. C.
Several patents teach the preparation of alkoxy ketones by high temperature dehydrogenation of alkoxy alkanols in the presence of different catalysts. Gremmelmaier, U.S. Pat. No. 4,141,919, Feb. 27, 1979, teaches the use of a copper-containing catalyst activated at high temperatures with hydrogen, wherein the reaction is run at temperatures from 90.degree. C. to 450.degree. C. Friedli, U.S. Pat. No. 3,462,495, Aug. 19, 1969, teaches the use of a calcium nickel phosphate catalyst at a temperature of 350.degree. C. to 450.degree. C.
Kaulen and Schafer, "Oxidation of Primary Alcohols to Carboxylic Acids at the Nickel Hydroxide Electrode", Synthesis, 513-516 (July, 1979), disclose that primary alcohols can be oxidized to carboxylic acids by electrolysis in a water and sodium hydroxide solution with a nickel hydroxide anode and a steel cathode. Vertes et al., "A New Method for the Electrochemical Oxidation of Alcohols", Tetrahedron, 28, 37-42 (1972), teach that primary alcohols, such as ethanol and benzyl alcohol, can be oxidized to aldehydes. Such oxidation takes place by electrolysis of a solution containing the primary alcohol and potassium hydroxide using a nickel hydroxide coated electrode.
Fleischman et al., "The Oxidation of Organic Compounds at a Nickel Anode in Alkaline Solution", J. Electroanal. Chem., 31, 39-49 (1971), teach that primary and secondary alcohols can be electrolyzed to prepare carboxylic acids and ketones using a nickel electrode. It is suggested therein that nickel hydroxide is prepared at the electrode. It is further suggested that such compound then oxidizes the primary of secondary alcohol. The possible preparation of nickel peroxide on the electrode is suggested.
British Pat. No. 1,051,614 teaches that a secondary alcohol can be oxidized to a ketone by electrolysis using a nickel electrode.
Ross et al., "Anodic Oxidation. IX. Anodic Oxidation of 2-Methoxyethanol", J.A.C.S., 95(7), 2193 (April, 1973), teach that electrolysis of 2-methoxyethanol in the presence of fluoroborate electrolytes results in the oxidation of the ether functionality rather than the alcohol functionality
A process for the preparation of ether ketones from (poly)propylene glycol monoethers wherein the hydroxy group is selectively oxidized without the oxidation of the ether functionality is desirable. It is also desirable to do such process at low temperatures.